PROJECT SUMMARY Dendritic cell (DC)-based therapeutic vaccines have shown the most promise for controlling HIV replication without antiretroviral therapy (ART). Although two seminal clinical trials demonstrated significant decreases in plasma viremia without ART that were associated with vaccine-induced HIV-specific immune responses, other DC-based vaccine studies have shown equivocal or no virologic efficacy. The disconnect between a DC-based vaccine's theoretical capability, supported by strong in vitro evidence of priming of effector T-cells, and the variable results of clinical trials, highlight important gaps in understanding the determinants of DC vaccine efficacy in vivo. We therefore propose a comparative analysis to confirm prior efficacy of DC vaccines and to test new, innovative DC vaccines with the dual goals of improving virological efficacy and identifying key determinants of DC vaccine efficacy. Specifically, we will conduct an initial phase I/II, randomized, double- blind, pilot study to compare safety and anti-HIV efficacy of four different DC-based vaccines and two corresponding placebos. The trial will evaluate two DC maturation techniques (the prostaglandin E2-matured DCs, which were partially effective in the two seminal clinical trials, and the alpha-type-1 DCs, which have shown improved antigen-presenting and T-cell priming function ex vivo), two HIV immunogens (whole, inactivated, autologous HIV that was partially effective in the two trials, and a pool of HIV peptides covering the most highly-conserved regions in Gag and Pol combined with epitopes known to be associated with control of viremia in untreated HIV-infected individuals), and two dosing strategies (3 vs 6 doses). The primary efficacy outcome will be change in the inducible HIV reservoir from pre-vaccination to 2 weeks after the final vaccine dose. We will also further evaluate the in vivo anti-HIV efficacy of the DC vaccines by performing an extensive analysis of vaccine-induced changes in virologic and immunologic parameters with the secondary goal of identifying immune correlates of vaccine-induced virologic responses. The parameters measured will include residual plasma viremia, the number and transcriptional activity of HIV-infected cells, CD8+ T-cell inhibition of autologous virus replication, the magnitude, breadth, and polyfunctionality of immune responses, and immunoregulatory responses including regulatory T-cells and myeloid-derived suppressor cells. We propose a second clinical trial to assess reproducibility of initial findings from the first trial and to assess the impact of further refinements of DC vaccine designs on efficacy. We have developed pre-specified Go/No-Go criteria for moving forward to a second trial. The decision whether a specific DC vaccine will be evaluated in the second trial will be based on the primary and secondary virologic and immunologic endpoints of the first trial. This innovative, sequential, and iterative approach will evaluate multiple DC vaccines, elucidate determinants of vaccine efficacy, identify immune correlates of vaccine-induced reductions in HIV reservoirs, and provide new insights into the potential for DC vaccines to achieve durable HIV remission without ART.